Apparatuses for automatically checking the position or the integrity of tools are often utilized in machine tools of various types as, for example, numeric control machining centers where the condition of the tools can be checked in the course of the actual machining phase when the tool is coupled to the rotating spindle.
Known apparatuses and methods perform checkings of this type, i.e. determine the presence, the position, the dimensions and possible breakages of tools, by utilizing feelers for contacting the tools, or contactless systems as, for example, optical systems that employ light rays or beams.
U.S. Pat. No. 3,912,925 discloses a drilling machine in which devices for checking the integrity of the tools utilize transversal light beams with limited thickness. The beams are substantially coplanar to the feed direction of the tools. The non-interruption of a light beam at a specific position of the tool is detected and notifies an anomalous condition of the tool.
Different applications of optical or optoelectronic systems for checking the position and/or the dimensions of non-rotating tools with profile not a priori precisely known present specific problems. This is the case, for example, when checking tools located in the tool-holder (“turret”) of a lathe and it is required to accurately check the position of the cutting edge of these tools.
A specific problem rises whenever expensive and delicate devices with thick linear sensors that employ an equally thick light beam enabling to detect and to analyze the entire profile of the tool (for example “shadow-casting” systems) cannot be used and it is desired to utilize apparatuses in which there is simply detected the interruption of a light beam (for example a laser beam) with limited thickness. The posed problem is to find the correct arrangement between tool and light beam that enables the former to interfere with the latter at the significative dimension to be checked, since the position of the significative dimension along the entire profile of the tool is not a priori known.
A solution proposed, for example, in U.S. Pat. No. 3,749,500 (FIG. 17, column 16, lines 4-21) is to arrange the optoelectronic apparatus in such a way that the beam lies in the plane that includes the profile of the tool to be checked, substantially perpendicular to the direction of the dimension to be checked. In many cases this possible solution is not applicable by reasons of insufficient room available. Moreover such solution is not really flexible because it does not enable to carry out checkings of different tools—for example, tools mounted in different positions on the same turret—the significative profile of which, i.e. the profile that includes the cutting edge to be checked, lies in different planes. Therefore, it is necessary to add complexity to the system by foreseeing the possibility of displacing the beam perpendicularly to the planes of the profiles or vice versa and to identify the correct position by performing an additional scan in said direction.
Furthermore, the checkings that the solution disclosed in U.S. Pat. No. 3,749,500 enables to perform are limited to a single direction along the significative profile plane, i.e. perpendicular to the light beam. This means the preclusion, unless arranging a plurality of light beams in other ways, to checkings of tools with cutting edges that include—as often occurs—conceptually punctiform working areas with different orientations along the significative profile plane.
Therefore, it is preferred to resort to a different arrangement of the optoelectronic apparatus, in which the light beam lies in a transversal direction (more particularly, a perpendicular direction) to the plane of the tool profile.
FIG. 1 schematically shows a cross-section view along plane X-Z of a mechanical part U that includes an end point C, along direction X, the position thereof is to be checked along the same direction X (checking direction). FIG. 1 also shows the cross-section view along the same plane X-Z of a light beam R arranged along a direction Y perpendicular to the plane X-Z. The mechanical part U schematically represents, for example, a tool mounted in the turret of a lathe and including, in a position along the plane X-Z not a priori known, a cutting edge C the position of which along the direction X is to be located.
A method of performing the checking foresees identifying the trend of the profile B—not a priori known—of the part U along the cross-section plane, by a point scan of the profile. If the tool to be checked is located in the turret of a lathe, the scan is performed, for example, by displacing the turret along directions X and Z according to sequences of a known type, by detecting interruptions of the light beam R at a plurality of points of the profile B, and by performing processings, also of a known type, including, for example, interpolations for locating points of the profile B not “contacted” by the beam R.
This known method may pose reliability problems bound to the selected scan interval, type of scan (greater or lesser number of points to be checked and consequent longer or shorter involved time) and consequent necessary processings. In fact, an inaccurate or incomplete detection of the profile may cause—in the formerly mentioned example—the missed identification of the point C of maximum projection in the direction X, the position of which has to be checked.
In any case, the known method is time consuming and involves complex processings.